The invention relates to a process for dispersing solids in a liquid phase.
It is known that solids can be dispersed in a liquid phase, for example pigments and fillers in a solution of a binder, in stirred ball mills by supplying mechanical energy. The stirred ball mills contain a grinding medium, for example sand, and the energy is supplied by the movement of rotors located in the stirred ball mill. In the dispersing processes used to date, 70 to 90% volume of the grinding chamber of the stirred ball mill is filled with sand. The mill base flows through the grinding chamber in an axial direction. The throughput of the mill base through the container is in general chosen so that the prescribed desired fineness is achieved after one or more passes. This procedure is frequently referred to as the one-pass or multi-pass procedure.
The level of production achievable by this procedure, that is to say the amount of finished mill base produced per hour, can be increased substantially if the procedure described in German Patent Specification 2,230,766 or German Laid-Open Application 1,902,152 is used. In this circulatory procedure, the throughput of mill base through the mill is high, and , after leaving the mill, the mill base flows back into a container, from which it is conveyed again into the mill by means of a pump. The same effect can be achieved if, using so-called pendulum procedure, the mill base flows through the stirred ball mill with high throughputs from one container into a second container. This process is repeated until the desired fineness is achieved.
Furthermore, it is known that the level of production can be increased when finer grinding media are used. In the circulatory procedure or pendulum procedure described, the high throughput of mill base causes relatively high drag forces to act on the fine grinding medium, which is then conveyed with the flow towards the grinding medium separating system of the stirred ball mill.
In these procedures, achieving a very hard-wearing seal for the moving parts of the stirred ball mill and separating off the grinding medium from the mill base leaving the stirred ball mill present problems. For the latter purpose, sieves are employed, these being exposed to a great deal of wear due to friction with the grinding medium.